deb-gnocchi/doc/source/configuration.rst

Configuration

Configure Gnocchi by editing /etc/gnocchi/gnocchi.conf. The configuration file should be pretty explicit, but here are some of the base options you want to change and configure:

Option name	Help
storage.driver	The storage driver for metrics.
indexer.url	URL to your indexer.
storage.file*	Configuration options to store files if you use the file storage driver.
storage.swift*	Configuration options to access Swift if you use the Swift storage driver.
storage.ceph*	Configuration options to access Ceph if you use the Ceph storage driver.

Gnocchi provides these storage drivers:

• File (default)
• Swift
• Ceph
• InfluxDB (experimental)

Gnocchi provides these indexer drivers:

• PostgreSQL (recommended)
• MySQL

Configuring the WSGI pipeline

The API server leverages Paste Deployment to manage its configuration. You can edit the /etc/gnocchi/api-paste.ini to tweak the WSGI pipeline of the Gnocchi REST HTTP server. By default, no authentication middleware is enabled, meaning your request will have to provides the authentication headers.

Gnocchi is easily connectable with OpenStack Keystone. If you successfully installed the keystone flavor using pip (see installation), you can edit the api-paste.ini file to add the Keystone authentication middleware:

[pipeline:main]
pipeline = keystone_authtoken gnocchi

Also, if you're planning on using CORS (e.g. to use Grafana), you an also add the CORS middleware in the server pipeline:

[pipeline:main]
pipeline = keystone_authtoken cors gnocchi

With or without Keystone support.

Driver notes

Carbonara based drivers (file, swift, ceph)

To ensure consistency across all gnocchi-api and gnocchi-metricd workers, these drivers need a distributed locking mechanism. This is provided by the 'coordinator' of the tooz library.

By default, the configured backend for tooz is file, this allows locking across workers on the same node.

In a multi-nodes deployment, the coordinator needs to be changed via the storage/coordination_url configuration options to one of the other tooz backends.

For example to use Redis backend:

coordination_url = redis://<sentinel host>?sentinel=<master name>

or alternatively, to use the Zookeeper backend:

coordination_url = zookeeper:///hosts=<zookeeper_host1>&hosts=<zookeeper_host2>

Ceph driver implementation details

Each batch of measurements to process is stored into one rados object. These objects are named measures_<metric_id>_<random_uuid>_<timestamp>

Also a special empty object called measures has the list of measures to process stored in its xattr attributes.

Because of the asynchronous nature of how we store measurements in Gnocchi, gnocchi-metricd needs to know the list of objects that are waiting to be processed:

• Listing rados objects for this is not a solution since it takes too much time.
• Using a custom format into a rados object, would force us to use a lock each time we would change it.

Instead, the xattrs of one empty rados object are used. No lock is needed to add/remove a xattr.

But depending on the filesystem used by ceph OSDs, this xattrs can have a limitation in terms of numbers and size if Ceph is not correctly configured. See Ceph extended attributes documentation for more details.

Then, each Carbonara generated file is stored in one rados object. So each metric has one rados object per aggregation in the archive policy.

Because of this, the filling of OSDs can look less balanced compared to RBD. Some objects will be big and others small, depending on how archive policies are set up.

We can imagine an unrealistic case such as retaining 1 point per second over a year, in which case the rados object size will be ~384MB.

Whereas in a more realistic scenario, a 4MB rados object (like RBD uses) could result from:

• 20 days with 1 point every second
• 100 days with 1 point every 5 seconds

So, in realistic scenarios, the direct relation between the archive policy and the size of the rados objects created by Gnocchi is not a problem.